Method for adjusting a seat

ABSTRACT

A synchronous tilt control mechanism is provided for a chair. The chair includes a base, a seat, a back, a torsion spring, a first slide member and a second slide member. The base further includes a tilt control housing mounted thereon. The back includes a forwardly extending support member. The seat and back are pivotally attached to the tilt control housing. The torsion spring has a forwardly extending leg and a rearwardly extending leg. The forwardly extending leg is mounted to the tilt control housing. The seat slidably engages the support member by way of the first slide member, which is disposed on one of the seat and the support member. The support member slidably engages the rearwardly extending leg of the torsion spring by way of the second slide member, which is disposed on one of the support member and rearwardly extending leg. A downward movement of the seat causes the back to move downwardly and rearwardly against an upward force provided by the torsion spring. During the downward movement, the back is moved downwardly and rearwardly at a slightly greater rate than the seat, whereby the comfort of the user is improved. A tilt limiter device is used to limit the upward tilting of the back. In a forward tilt position, the movement of the back is arrested, whereby the seat is permitted to tilt forwardly and upwardly by itself. The seat and back can also be maintained in a plurality of positions by a tilt lock device. The seat can also be maintained in a forward tilt position by a stop device. In addition, a seat adjustment device can be employed to allow for forward and rearward adjustment of the seat.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to tilt controlmechanisms for chairs, and in particular, to synchrotilt controlmechanisms.

[0002] In general, tilt control mechanisms are mechanical devices thatcontrol the tilting of a chair when occupied by a user. To provideimproved aesthetics, and to avoid interference with use of the chair,tilt control mechanisms are typically mounted underneath the chair. Tiltcontrol mechanisms also typically employ a spring, or other energystoring device, to control the rate at which the chair tilts and toreturn the chair to an upright position when the user is not leaningback in it. Tilt control mechanisms generally include an adjustmentdevice that permits the user to vary the upward force exerted by thespring, thereby allowing the chair to tilt downwardly and rearwardlymore or less easily depending on the upward force exerted.

[0003] Tilt chairs come in a variety of forms, although most include aseat and a back. For example, some tilt chairs have a seat maintained ina fixed position, allowing only the back to tilt rearwardly anddownwardly. In another form, tilt chairs have the seat and back rigidlyconnected whereby they tilt rearwardly and downwardly at the same rate.Both of these types of chairs have disadvantages. For example, a fixedseat and back arrangement does not allow the user's body cavity to openup as the user tilts rearwardly. An open body cavity allows for bettercirculation and spinal curvature, thereby improving the user's comfortand physical health. Moreover, many of the previous designs pivot abouta point near the base or support of the chair where the user's center ofgravity is located. As a result, when the chair is tilted rearwardly,the user's feet are lifted off of the floor by the front part of theseat, thereby generating pressure on the underside of the user's thighs,making the user uncomfortable and inhibiting the user's circulation.Synchrotilt control mechanisms were designed to overcome some of theseproblems.

[0004] With synchrotilt mechanisms, the back and seat tiltsimultaneously, but at different rates. Generally, the back tilts at afaster rate than the seat so that the body cavity opens. An example of aprior synchronous tilt control mechanism may be found in U.S. Pat. No.4,390,206, entitled Synchrotilt Chair Control and issued to Faiks, et.al.

[0005] Typically, synchrotilt chairs have the seat and backinterconnected so as to actuate the synchronized tilting of the backwith the seat. For example, the seat and back may be directly pivotallyconnected as set forth in the Faiks, et. al. Patent. Other synchrotiltcontrol mechanisms employ linkage mechanisms to interconnect the seatand back and to actuate the synchronous tilting. In either type, thesynchrotilt control mechanism comprises complex interconnecting movingparts. The majority of these prior art tilt control mechanisms permitonly backward tilting of the chair, separately or together at differingrates. To counter that problem, U.S. Pat. No. 5,029,940, entitled ChairTilt and Chair Height Control Apparatus and issued to Golynsky,discloses a tilt mechanism permitting both forward and backward tiltingof the chair seat and back using the same mechanism. That mechanism usesa four-bar linkage mechanism, whereby the seat is interconnected withthe back. When the seat is tilted upwardly, the back of the chair isalso caused to be tilted upwardly. Accordingly, the back can protrudeinto the user's back thus making use in the forward tilt positionuncomfortable.

SUMMARY OF THE INVENTION

[0006] Briefly stated, the invention is directed to a chair adapted forsynchronous tilting between an upright position and a reclined position.In one aspect, the chair has a base, a tilt control housing, a seat, aback, a torsion spring, a first slide member, a second slide member anda tilt limiter device. The tilt control housing is mounted to the base.The seat is pivotally attached to the tilt control housing about a firsthorizontal axis. The back is pivotally attached to the tilt controlhousing about a second horizontal axis positioned rearwardly of thefirst horizontal axis. The back includes a forwardly extending supportmember. The torsion spring has a forwardly extending leg mounted to thetilt control housing and a rearwardly extending leg. The first slidemember is disposed on one of the seat and support member and slidablyengages the other of the seat and support member. The second slidemember is disposed on one of the support member and the rearwardlyextending leg of the torsion spring and engages the other of the supportmember and rearwardly extending leg. The tilt limiter device is adaptedto limit upward tilting of the back.

[0007] Another aspect of the invention is to provide a tilt lock deviceto releasably lock the chair in a plurality of positions, including anupright position and a reclined position. The tilt lock device includesa lock member, a guide member having a guide hole and a lock pinslidably received in the guide hole. The lock member has a plurality ofopenings adapted to receive the lock pin and extends downwardly from theback support member. The guide member is mounted to the tilt controlhousing. When the tilt lock device is activated, the lock pinselectively engages the lock member at one of the openings.

[0008] In another aspect of the invention, the chair is adapted topermit a forward tilting of the seat without a corresponding forwardtilting of the back. In a preferred embodiment, the seat can bemaintained in the forward position by securing the seat with a stopdevice Because the seat is not linked to the back, but only slidablyengages it by way of the first slide member, the forward tilting of theseat does not simultaneously cause a forward tilting of the back. Theback, therefore, does not protrude into the user's back or otherwiseinterfere with the space located above the forwardly tilted seat.

[0009] Another aspect is for the horizontal axis of the torsion springto be spaced apart from the second horizontal axis of rotation.Preferably, the axis of the spring is positioned below the second axisof rotation of the back such that the torsion spring exerts anincreasingly greater upward force to counter any shift in the center ofgravity of the user as the chair tilts rearwardly.

[0010] Yet another aspect of the invention is a seat depth mechanism,which permits the user to adjust the forward and rearward position ofthe seat with respect to the back of the chair. The mechanism includes ashell slidably attached to a seat bracket, a lever, a spring and afastener. The shell includes a housing. The seat bracket has anadjustment slot and a plurality of teeth. The lever is disposed in thehousing and is adapted to operably engage the spring which is alsodisposed in the housing. The lever is also adapted to engage the teethof the seat bracket. When the lever is disengaged from the teeth, theuser can slide the shell forward and rearward on the seat bracket untila desired positioning of the shell is achieved. When the lever isreleased by the user, the spring biases the lever inwardly to engage theteeth of the seat bracket, thereby preventing the shell from sliding inthe forward or rearward direction.

[0011] The present invention provides significant advantages over othersynchronous tilt mechanisms in that the synchronous tilt mechanism issimplified by using two slide members without the need for a complicatedlinkage mechanism. Furthermore, the tilt mechanism provides a device forlocking the back and seat in a variety of positions. Finally, thesimplified slide mechanism permits the seat of the chair to tiltforwardly and upwardly without the corresponding forward tilt of theback.

[0012] The present invention, together with further objects andadvantages, will be best understood by reference to the followingdetailed description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a perspective view of an office chair with the tiltcontrol mechanism applied thereto.

[0014]FIG. 2 is a top view of an office chair taken along line 2-2 ofFIG. 1 with a preferred embodiment of the tilt control mechanism appliedthereto, including a tilt lock device and a seat lock device.

[0015]FIG. 2A is a partial top view similar to FIG. 2 except that acoupling bracket is shown instead of the seat lock device.

[0016]FIG. 2B is a partial side view taken along line 2B-2B of FIG. 2A.

[0017]FIG. 2C is a sectional view taken along line 2C-2C of FIG. 2B.

[0018]FIG. 3 is a cross-sectional view of the tilt control mechanismtaken along line 3-3 of FIG. 2.

[0019]FIG. 4 is a cross-sectional view of the chair in an uprightposition taken along line 4-4 of FIG. 2 except that a coupling block isshown instead of the seat lock device.

[0020]FIG. 4A is a partial sectional view similar to FIG. 4 except thatthe first slide member is disposed on the back support member.

[0021]FIG. 4B is a partial sectional view similar to FIG. 4A except thatthe second slide member is disposed on the rearwardly extending leg ofthe torsion spring.

[0022]FIG. 4C is a partial sectional view similar to FIG. 4 except thatthe second slide member is disposed on the rearwardly extending leg ofthe torsion spring.

[0023]FIG. 5 is a cross-sectional view of the tilt control mechanismsimilar to FIG. 4 except that the chair is located in a reclinedposition.

[0024]FIG. 6 is a cross-sectional view of the tilt control mechanismtaken along line 6-6 of FIG. 2 with the chair located in an uprightposition.

[0025]FIG. 7 is a cross-sectional view of the tilt control mechanismsimilar to FIG. 6 except that the chair is located in a reclinedposition.

[0026]FIG. 8 is a cross-sectional view of the tilt control mechanismtaken along line 8-8 of FIG. 2 with the chair located in an uprightposition.

[0027]FIG. 9 is a cross-sectional view of the tilt control mechanismsimilar to FIG. 8 except that the seat is located in a forward positionand the back is locked in an upright position.

[0028]FIG. 10 is a partial bottom view of the tilt control mechanismtaken along line 10-10 of FIG. 6.

[0029]FIG. 11 is a top view of the seat with a seat adjustment deviceapplied thereto.

[0030]FIG. 12 is a cross-sectional view of the seat adjustment devicetaken along line 12-12 of FIG. 11 with the lever located in an engagedposition.

[0031]FIG. 13 is a cross-sectional view of the seat adjustment devicesimilar to FIG. 12 except that the lever is located in a disengagedposition.

[0032]FIG. 14 is a cross-sectional view of the seat taken along line14-14 of FIG. 11.

[0033]FIG. 15 is a schematic showing the relative positioning of theback and seat in a reclined position, an upright position and a forwardtilt position.

[0034]FIG. 16 is an exploded view of the tilt control mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Referring to the drawings, FIGS. 2, 4 and 6 show a synchronoustilt chair 1 including a base 2, a seat 4, a back 5, a torsion spring 7,a first slide member 10, and a second slide member 11. Mounted to thebase 2 is a tilt control housing 3. The seat 4 is pivotally attached tothe tilt control housing 3 using a first pivot member 101. The back 5 ispivotally attached to the tilt control housing 3 using a pair of secondpivot members 102, as shown in FIGS. 2 and 3. The seat 4 rotates about afirst axis of rotation 12 and the back 5 rotates about a second axis ofrotation 13. The first and second axis of rotation 12 and 13 aregenerally parallel. In a preferred embodiment, the first axis ofrotation 12 is positioned forward of the second axis 13 as shown inFIGS. 2, 4 and 6 so as to provide for synchronous tilting of the seatand the back.

[0036] As shown in the FIG. 15 schematic, the seat 4 is positionedrelative to a horizontal plane at an angle designated by the Greekletter alpha (α) when the chair is in an upright position. Similarly,the back 5 is positioned relative to the horizontal plane at an angledesignated by the Greek letter beta (β). In a preferred embodiment, α isabout five degrees and β is about ninety-five degrees. When the firstaxis of rotation 12 is positioned forward of the second axis of rotation13, the seat 4 rotates through a first angle, designated as α1, as theback 5 rotates through a greater second angle, designated as β1. In apreferred embodiment, α1 is about 12.5 degrees and β1 is about 20.5degrees, thereby providing a 1.64:1 tilt ratio. It should be understoodthat a change in position of the first axis of rotation relative to thesecond axis of rotation will correspondingly change the tilt ratio. Atilt ratio in the range of about 1.5:1 to 2.0:1 will generally provide acomfortable tilting action for a user. The synchronous tilting of theseat 4 and back 5 permits the user's body cavity to open as the usertilts rearwardly and thereby contributes to the increased comfort of theuser.

[0037] As shown in FIGS. 2, 4 and 6, the back 5 generally includes aforwardly extending support member 6 positioned below the seat 5. In apreferred embodiment, shown in FIG. 4, a first slide member 10 isfixedly mounted to the seat 4 and slidably engages the support member 6.In the preferred embodiment, the first slide member 10 has an arm 85 anda tab 87. The arm 85 wraps around an edge 89 of the seat 4 and the tab87 is disposed in a hole 91 in the seat 4. The arm 85 can be liftedupwardly so as to disengage the tab 87 from the seat 4, whereby thefirst slide member 10 can be removed and replaced easily andinexpensively.

[0038] In alternative embodiments, the first slide member can be made anintegral part of the seat or support member, or it can be a separatemember, but more permanently mounted, such as by bonding. As shown inFIGS. 4A and 4B, the first slide member 10 can also be mounted on a topsurface 21 of the support member 6 and adapted to slidably engage theseat 4.

[0039] It is recognized that one or more first slide members 10 may beused to support and slidably engage the seat 4 and support member 6. Forexample, the preferred embodiment shown in FIG. 2 employs a pair offirst slide members 10. By using a pair of first slide members 10, thecontact surface area between the first slide members 10 and the seat 4and support member 6 is greatly increased, thereby distributing the loadmore evenly between the seat 4 and support member 6 and reducing largepoint loads and resulting stresses in the seat 4 and support member 6.In a preferred embodiment, the first slide members 10 are made out ofacetal. Hoechst Celanese produces a commercially available acetalmaterial designated M90 CELCON. Acetal exhibits excellent wearcharacteristics, yet provides a good sliding interface with the seat orsupport member, which are preferably made out of steel.

[0040] As shown in FIGS. 2 and 3, a pair of torsion springs 7 is used tosupport the seat 4 and back 5. The springs 7 are disposed on a shaft 78.Each torsion spring 7 has a forwardly extending leg 8 adjustably mountedto the tilt control housing 3 as shown in FIGS. 4 and 6. Each torsionspring 7 also has a rearwardly extending leg 9 which slidably engages asecond slide member 11.

[0041] To accommodate the various weights of different users, anadjustment knob 15 can be used to vary the amount of upward forceexerted by the torsion springs 7. For example, the adjustment knob 15can tighten the torsion springs 7 by operably engaging and forcingdownward an adjustment bar 25. The adjustment bar 25 is positioned inguide slots 23 located in the tilt control housing 3 as shown in FIGS. 4and 5. The adjustment bar 25 engages the forwardly extending legs 8 ofthe torsion springs 7. When tightened, the adjustment knob 24 operablyengages a screw 26 extending upwardly from the adjustment knob 24. Theadjustment knob 24 is adapted to receive the screw 26 as it movesdownwardly. The screw 26 is mounted to an adjustment bracket 91 whichengages the adjustment bar 25. As the adjustment knob 24 turns thescrew, causing it to move downwardly within a hole located in theadjustment knob 24, the adjustment bar 25 moves downwardly in the guideslots 23, thereby increasing the torque of the torsion springs 7.Correspondingly, a greater upward force is exerted by the ends of therearwardly extending legs 8 of the torsion springs 7 against the secondslide member 11. In this way, the user can adjust the amount of upwardforce exerted against the seat 4 and user. If it is desirable to have agreater force exerted, i.e., to accommodate heavier users, theadjustment knob 25 provides a simple way of varying the resistant upwardforce. A wide variety of user weights may therefore be accommodated.Similarly, if a user wishes to have greater or lesser spring resistancein order to give a firmer or softer feel to the chair, respectively,they can adjust the torsion spring accordingly.

[0042] Preferably, the second slide member 11 is disposed on theunderside 19 of the support member 6 and slidably engages the rearwardlyextending legs 9 of the torsion springs 7 which have end portions 77coupled together by a block member 14, as shown in FIG. 4.Alternatively, the second slide member can slidably engage therearwardly extending legs without a block member interposed between theslide member and legs. In another embodiment, the second slide member 11is disposed on the rearwardly extending legs 9 of the torsion springs 7and slidably engages, as illustrated in FIGS. 4B and 4C, the underside19 of the support member 6. In this embodiment the second slide member11 couples together the rearwardly extending legs 9 and is configured asthe aforementioned block member.

[0043] In the preferred embodiment of FIG. 4, the second slide member 11is mounted to the support member 6 in such a way as to make it removableand therefore easily replaceable. In the preferred embodiment, therearwardly extending legs 9, disposed in the block member 14, slidablyengage the second slide member 11 which is mounted to the support member6 as shown in FIGS. 4 and 5. As with the first slide member 10, thesecond slide member 11 is preferably made out of acetal.

[0044] To provide an optimal sliding interface between the second slidemember 11 and the block member 14, the block member 14 is preferablymade out of nylon. The second slide member 11 and the block member 14are configured as complementary wedge-shape members, illustrated inFIGS. 4 and 5, so as to ensure that maximum contact is maintainedbetween the block member 14 and the second slide member 11 as the seat 4and back 5 tilt rearwardly. In addition, the block member 14 has aforwardly extending flange 171. The flange 171 has a hole 173 and ismounted on a shaft 78 between the torsion springs 7 as shown in FIG. 4.

[0045] As a user tilts rearwardly, the center of gravity of the usermoves rearwardly. Accordingly, the lever arms between the applied forceof the user's weight and the reaction force at the rearwardly extendinglegs 9 of the torsion springs 7 and the reaction force at the secondpivot members 102, located at the second axis of rotation 13, areincreased proportionately. However, the increased force applied to thetorsion springs 7 at the point of contact between the second slidemember 11 and the rearwardly extending leg 9 of the torsion springs 7 iscountered by an increased force applied upwardly by the rearwardlyextending legs 9. The increased upward force is caused by a shorteningof the lever arm between the point of contact and the horizontal axis ofthe torsion springs as the second slide member 11 disposed on thesupport member 6 slides forwardly on the block member 14. The axis ofthe springs 7 is approximately the same as the axis of the shaft 78 onwhich the springs 7 are disposed.

[0046] As shown in FIGS. 4 and 5, the sliding contact between the blockmember 14 and the second slide member 11 moves forward as the chairmoves from the upright position to the reclined position. This forwardlysliding contact results from the springs' axis being positioned belowthe second axis of rotation 13. As the distance between the point ofcontact and the axis of the springs' rotation decreases, the lever armof the torsion springs 7 is reduced and a correspondingly greater upwardforce is produced by the rearwardly extending legs 9. This increasedupward force of the torsion springs 7 counters the aforementionedincreased downward force produced by the user shifting his weightrearwardly. Thus, by offsetting the axis of the springs 7 from thesecond axis of rotation 13, a tilt control mechanism is provided whichautomatically adjusts for the increased moment arm, and resultant force,produced by a shift in the center of gravity as a user moves the chairbetween an upright position and a reclined position. As a result, theuser does not feel a sag or decreased resistance as the chair is tiltedinto the reclined position.

[0047] As shown in FIGS. 4 and 6, the tilt control mechanism also has atilt limiter device 15. The tilt limiter device 15 limits the upwardtilting of the back 5. The tilt limiter device 15 has a stop member 16depending downwardly from the support member 6 of the back 5, and acatch member 17 disposed on the tilt control housing 3. The stop member16 is adapted to engage the catch member 17 when the torsion spring 7biases the stop member 16 against the catch member 17 by way of thesecond slide member 11 and support member 6, thereby preventing the back5 from rotating past the upright position. In the preferred embodiment,the stop member 16 is configured as a hook. In an alternativeembodiment, the stop member can depend downwardly from the seat. In suchan embodiment, the seat is prevented from rotating past an uprightposition. Because the torsion spring biases the support member upwardlyagainst the seat, the back is also prevented from rotating past theupright position. In yet another embodiment, the tilt limiter device canbe adapted to interconnect the seat and back, whereby the relativemotion of the seat and back causes the tilt limiter device to arrest thechair at an upright position.

[0048] The tilt control mechanism described in the foregoing embodimentsoperates in several different ways. For the purpose of illustration, theoperation of the chair 1 will be described in terms of the varioussitting positions that the preferred embodiment of FIGS. 6-10 mayaccommodate. For example, the chair 1 assumes an upright position whenunoccupied or when a user is sitting in an upright position, as shown inFIGS. 6 and 8. When in this position, the seat is positioned at an angleα and the back is positioned at an angle β, as illustrated in the FIG.15 schematic. The chair 1 can also be reclined, or assume a reclinedposition, as shown in FIGS. 7. When in this position, the seat ispositioned at an angle α1 and the back is positioned at an angle β1.Alternatively, the seat 4 can be positioned in a forward tilt positionas shown in FIG. 9. In a forward tilt position, the seat 4 rotatesforwardly while the back 5 is maintained between the upright andreclined positions. As shown in FIG. 15, the seat 4 is positioned at anangle α2. Preferably, the chair can accommodate any number of positionsnot specifically identified and interspersed between the aforementionedpositions.

[0049] When the chair is in the upright position, as shown in FIGS. 4, 6and 8, the first slide members 10 engage the support member 6. Thesecond slide member 11, preferably configured as a wedge shaped member,slidably engages the wedge shaped block member 14, which couples thetorsion spring end portions 77. The torsion spring 7 exerts an upwardforce against the second slide member 11, thereby supporting the supportmember 6 and the seat 4. The torsion spring 7 also biases the stopmember 16 against the catch member 17. Because the tilt limiter device15 prevents the back 5 from being tilted forwardly and upwardly past thepoint where the stop member 16 engages the catch member 17, the back 5and seat 4 are biased into the upright position.

[0050] When a user occupies the chair 1 in an upright position, as shownin FIGS. 4, 6, and 8, they are supported by the seat 4. The seat 4, inturn, is supported by the tilt control housing 3 at the point of pivotalattachment and by the first slide member 10 slidably engaging thesupport member 6 of the back 5. The downward force applied by the firstslide member 10 to the support member 6 causes the second slide member11 to slidably engage the block member 14 coupling the end portions 77of the rearwardly extending legs 9 of the torsion spring 7. Thus, theuser's weight is carried and resisted by the torsion spring 7 by way ofthe seat 5, the first slide member 10, the support member 6 and thesecond slide member 11.

[0051] When a user reclines in the chair 1 as shown in FIGS. 5 and 7,the seat 4 is supported by the support member 6 by way of the firstslide members 7, which slidably engage the support member 6. Whenreclining, the first slide member 10 slides along the support member 6while the second slide member 11, mounted on the support member 6,simultaneously slides along the block member 14 coupling the endportions 77 of the rearwardly extending legs 9 of the torsion spring 7.As the seat 4 moves downwardly, the back 5 is caused to move downwardlyand rearwardly about its axis, whereby the user's feet are less likelyto be lifted off of the floor and a more comfortable seating arrangementis maintained. As the seat 4 and back 5 are rotated about the first andsecond horizontal axes 12 and 13, the stop member 16 is released ordisengaged from the catch member 17.

[0052] As shown in the preferred embodiment of FIGS. 6 and 10, a tiltlock device 28 is provided to lock the back 5 into a plurality ofpositions, including the upright position and the reclined position.When locked, the user can use the chair 1 in a fixed position without acorresponding tilting of the back 5 and seat 4. As shown in FIGS. 6 and10, the tilt lock device 28 has a lock member 29, a guide member 31, alock pin 30, an actuator spring 32, a disengagement spring 34 and an endbracket 33. The lock member 29 depends downwardly from the supportmember 6 and includes the stop member 16 in the preferred embodiment. Asshown in FIG. 6, the stop member 16, configured as a hook, is adapted toengage the catch member 17 disposed on the tilt control housing 3.

[0053] The lock member 29 also has a plurality of openings and a bottomedge 37. In a preferred embodiment, the lock member 29 has an upper slot35 and a lower slot 36 as shown in FIGS. 6 and 9. In other embodiments,the openings can be configured in a variety of different shapes.Moreover, the plurality can comprise a multitude of openings,corresponding to the desired number of fixed positions for the chair.

[0054] The guide member 31 has a cavity 38 and a guide hole 39. The lockpin 30 is received in the guide hole 39 and extends through the cavity38 as shown in FIG. 10. The disengagement spring 34 is disposed on aportion of the lock pin 30 which extends through the cavity 38. A lockwasher 41 is mounted on the portion of the lock pin 30 located insidethe cavity 38 in order to retain the lock pin 30 in the guide member 31and to capture the disengagement spring 34 between the lock washer 41and a bearing wall 40 defining one side of the cavity 38. The guidemember 31 is mounted to the tilt control housing 3 adjacent to the lockmember 29 and is oriented such that the lock pin 30 is positionedsubstantially perpendicular to the lock member 29.

[0055] A tilt lock cable 42 is attached at one end to a handle 43 whichincludes a housing 151 and a bracket 153. The handle 43 is slidablyattached to the first pivot member 101 as shown in FIGS. 2 and 3. Thefirst pivot member 101 extends outwardly from a front portion 44 of theseat at the first axis of rotation 12. The other end of the tilt lockcable 42 is attached to the actuator spring 32. The tilt lock cable 42is disposed in a cable guide 111 having one end mounted to the tiltcontrol housing 3 and the other end mounted to a forward portion of theseat 4 as shown in FIGS. 2 and 10. The actuator spring 32 interconnectsthe tilt lock cable 42 and the end bracket 33.

[0056] To actuate the tilt lock device 28, a user pulls the handle 43outwardly to a first level. The tilt lock cable 42, connected to thehandle 43, extends the actuator spring 32, which in turn applies ainward force to the end bracket 33. The end bracket 33 transfers theforce to the lock pin 30 and biases the lock pin 30 against the lockmember 29. For proper operation, the actuator spring 32 must exert ainward force on the lock pin 30, through the end bracket 33, that isgreater than the outward force exerted on the lock pin 30 by thedisengagement spring 34, because the disengagement spring 34 andactuator spring 32 simultaneously exert opposing forces on the lock pin30. If the outward force exerted by the disengagement spring 34 weregreater, the lock pin 30 could never be engaged with the lock member 29.Therefore, the disengagement spring 34 must be weaker than the actuatorspring 32. When the handle 43 is returned to its original position, theactuator spring 32 is relaxed and the disengagement spring 34 biases thelock pin 30 away from the lock member 29.

[0057] The actuator spring 33, when actuated, biases the lock pin 30against the lock member 29. As the user tilts forward or backward, anend of the pin 79 slides against the lock member 29. Eventually, theposition of the openings 35 and 36 corresponds to the position of thelock pin 30 whereby the lock pin 30 extends inwardly to engage the lockmember 29 at one of the openings 35 and 36.

[0058] Alternatively, as shown in FIGS. 6 and 10, the bottom edge 37 ofthe lock member 29 can slide past the lock pin 30, thereby permittingthe lock pin 30 to be extended inwardly to engage the bottom edge 37.When so positioned, the actuator spring 33 biases the lock pin 30 pastthe bottom edge 37, thus securing the lock member 29 to the tilt controlhousing 3. When engaged with the lock member 29 at the bottom edge 37 orat one of the slots 35 and 36, the lock pin 30 locks the back 5 andsupport member 6 into a certain position. In the preferred embodimentshown in FIGS. 6-9, the back 5 and support member 6 can be locked intoone of three positions. First, as shown in FIG. 7, the lock pin 30 isreceived within the upper slot 35 of the lock member 29, thereby lockingthe back 5 and support member 6 into a reclined position. Similarly, thelock pin can be received in the lower slot, thereby locking the back andsupport member into an intermediate position. Finally, as shown in FIG.6, the lock pin 30 can engage the bottom edge 37 of the lock member 29,thereby locking the back 5 and support member 6 into an uprightposition. In the upright position, the back 5 is prevented from movingdownwardly and rearwardly by the lock pin 30, which engages the bottomedge 37 of the lock member 29. The back 5 is also prevented from movingupwardly by the stop member 16, which engages the catch member 17.

[0059] It should be noted that an unoccupied chair will not disengagefrom a locked reclined or intermediate position, even if the handle 43is returned to its original position, because the torsion springs 7exert an upward force on the support member 6. Accordingly, the lockmember 16 exerts a corresponding upward force on the lock pin 30, whichis received in one of the slots 35 and 36. That force, in turn, createsa corresponding lateral friction force between the lock member 29 andthe lock pin 30, which prevents the lock pin 30 from disengaging fromthe lock member 29. The friction force exerted on the lock pin 30 by thelock member 29 is not overcome by the outward force exerted by thedisengagement spring 34. Thus, the chair has a built in safety devicewhich prevents the accidental springing forward of the back of anunoccupied chair when the handle 43 is disengaged. To the contrary, whena chair is occupied, the natural weight of the user counters the upwardforce of the torsion springs 7 and the corresponding upward forceexerted by the lock member 29 on the lock pin 30 is greatly reduced oreven eliminated. Accordingly, the resulting friction force applied tothe lock pin 30 by the lock member 29 is also reduced or eliminated andthe disengagement spring 34 is able to bias the lock pin 30 away fromthe lock member 29 when the handle is returned to its original position.

[0060] In a preferred embodiment, the seat 4 can also be positioned in aforward tilt position as shown in FIG. 9. As shown in FIG. 15, the seat4 rotates upwardly through an angle α2 to reach the forward tiltposition. In a preferred embodiment, α2 is about ten degrees. In thisposition, the first slide member 10 mounted on the seat 4 disengagesfrom the support member 6 as the seat 4 pivots upwardly about the firsthorizontal axis 12. A front torsion spring 49, shown in FIGS. 2 and 9,biases the seat 4 upwardly. The spring 49 is disposed on the first pivotmember 101. Alternatively, two springs can be disposed on the firstpivot member. The front torsion spring 49 has a first leg 50 and asecond leg 51. The first leg 50 is biased against a front portion of theseat 4. The second leg 51 is mounted to the tilt control housing 3. In apreferred embodiment, the back 5 is maintained in a locked position bythe tilt lock device 28 when the seat 4 is positioned in a forward tiltposition. However, the seat can be positioned in a forward tilt positionwithout the back or support member being in a locked position. In suchan embodiment, the seat is positioned in a forward tilt position, butcan tilt rearwardly with the back. In the preferred embodiment, itshould be understood that the back 5 and support member 6 can be lockedin any one of the three locked positions, i.e., a reclined position, anintermediate position, or an upright position, when the seat 4 is tiltedinto a forward tilt position. For example, the support member 6 islocked into an upright position in FIG. 9. When the back is in a lockedposition, or unlocked and retained in an upright position by the tiltlimiter device, the user is permitted to use the seat in a forward tiltposition without having the back 5 simultaneously rotate upwardly andprotrude into the user's back or otherwise interfere with the spaceoccupied above the forwardly tilted seat 4.

[0061] In a preferred embodiment, the seat 4 can be locked or held inthe forward tilt position by engaging a stop device. This permits theuser to be supported by the seat 4 when it is secured in the forwardtilt position.

[0062] The stop device operably engages the seat 4 and the tilt controlhousing 3 when the seat 4 is in a forward tilt position. The stop deviceincludes the tilt lock device 28 and a seat lock device 105. The seatlock device 105 includes a tilt bracket 52 and a lock bar 47. In thepreferred embodiment, the lock bar 47 comprises a rod. The tilt lockdevice 28 secures the back 5 to the tilt control housing 3 and the seatlock device 105 secures the seat 4 to the support member 6. As shown inFIG. 2, the lock bar 47 is preferably Y-shaped and has a pair of arms48. The tilt bracket 52 depends downwardly from the seat 4 and has afirst slot 54, a second slot 53 and a channel 55 communicating with theslots as shown in FIGS. 8 and 9. The support member 6 has a support slot56 positioned in a downwardly extending flange 107 as shown in FIG. 16.The arms 48 of the lock bar 47 are disposed in the support slot 56 andone of the openings of the tilt bracket 52. A pair of springs 57 biasthe lock bar 47 forwardly into one of the openings of the tilt bracket52. The springs 57 operably engage the lock bar and a forward edge 109of the support member 6. Alternatively, compression springs can be usedto bias the lock bar forwardly.

[0063] When the seat 4 is maintained between the upright and reclinedposition, the springs 57 bias the arms 48 of the lock bar 47 into thesecond slot 53 as shown in FIG. 8. The arms 48 are positioned in thesupport slot 56 and slidably engage the flange 107 of the back supportmember 6. The arms 48 are also positioned in the second slot 53 andslidably engage the tilt bracket 52, allowing the seat 4 and the back 5to tilt synchronously, yet maintaining a proximate relationship betweenthe seat 4 and back 5. This prevents the seat 4 from popping forward ifthe user applies a force to a point of the seat 4 forward of itshorizontal axis of rotation 12. In addition, the lock bar 47 preventsthe seat 4 from rotating forwardly due to the upward force applied bythe front torsion spring 49. Because the seat 4 is secured to thesupport member 6, the seat 4 can only rotate upwardly with the back 5.However, since the tilt limiter device 15 prevents the back 5 fromtilting upwardly past the upright position, the seat 4 is also preventedfrom doing so.

[0064] As shown in FIGS. 2A-2C, a coupling block 27 can also be employedto slidably connect the seat 4 to the support member 6 instead of thelock bar 47. In this embodiment, which does not employ a seat lockdevice, the seat 4 cannot be rotated into a forward tilt position. Thecoupling block 27 is mounted to the seat 4 as shown in FIGS. 2A-2C andslidably engages the flange 107 depending downwardly from the undersideof the support member 6. The coupling block 27 allows the seat 4 and theback to tilt synchronously, yet maintains the seat 4 in a proximaterelationship to the back. As previously explained with the preferredembodiment, which employs the lock bar to interconnect the seat andback, the coupling block 27 prevents the seat 4 from popping forwardwhen a force is applied forward of the seat's pivotal attachment 12.Rather, the seat's 4 upward motion is limited by the motion of thesupport member 6 due to the coupling block 27. Preferably, the couplingblock 27 is made out of nylon.

[0065] When a user wishes to use the seat 4 in a forward tilt position,an actuator device is employed. The actuator device includes a seat lockcable 63 attached to the handle 43, a slide bracket 59 and a lever arm60 attached to the seat lock cable 63 as shown in FIG. 2. The seat lockcable 63 is disposed in a cable guide 112 which is mounted to the rearportion of the support member 6 and to a forward portion of the seat 4as shown in FIGS. 2 and 16. The lever arm 60 is rotatably mounted to arear portion of the support member 6 and has a first end 61 engaging aslot in the slide bracket 59 and a second end 62 connected to the seatlock cable 63. The slide bracket 59 is slidably attached to the supportmember 6 with two pins and has a hook end connected to the lock bar 47.

[0066] To actuate the actuator device, the handle 43, which is slidablyattached to the first pivot member 101, is pulled outwardly, retractingthe seat lock cable 63 and rotating the lever arm 60. The rotation ofthe lever arm 60 causes the slide bracket 59 to translate rearwardly.The translation of the slide bracket 59 disengages the lock bar 47 fromthe second slot 53 in the side bracket 52 and translates the lock bar 47rearwardly in the support slot 56. As the lock bar 47 disengages fromthe second slot 53, the lock bar 47 moves into the channel 55 and thetorsion springs 49 bias the seat 4 upwardly until it reaches a forwardtilt position. If the handle 43 is released, the springs 57 bias thelock bar 47 into the first slot 54, translating the lock bar 47forwardly in the first slot 54 and the support slot 56. It is recognizedthat a release of the handle 43 at any point in the upward rotation willcause the lock bar 47 to move forward into the first slot 54 when theseat reaches the forward tilt position due to the force exerted by thesprings 57. Once positioned in the first slot 54, the lock bar 47slidably engages the tilt bracket 52 and support member 6, securing theseat 4 to the support member 6 and locking the seat 4 in the forwardtilt position.

[0067] To disengage the seat lock device 105, the user merely pulls thehandle 43, which causes the actuator device to translate the lock bar 47rearwardly from the first slot 54 into the channel 55 and translates thelock bar 47 rearwardly in the support slot 56 in the support member 6.Once the lock bar 47 is in the channel 55, a downward force on the seat4 causes the seat 4 to return to an upright position as the lock bar 47translates upwardly in the cannel 55. Once the seat 4 reaches theupright position, the springs 57 pull the lock bar 47 forwardly from thechannel 55 into the second slot 53. The lock bar 47 secures the upwardtilt bracket 52 to the support member 6.

[0068] The same handle 43 is used to activate both the tilt lock device28 and the actuator device 58 in the preferred embodiment. This servestwo purposes. First, a single handle provides improved aesthetics byavoiding a cluttering of the underside of the chair. Second, a singlehandle ensures that the preferred embodiment stop device is properlyactivated. The preferred stop device includes both the tilt lock device28 and the seat lock device 105. The stop device ensures that the seat 4is secured in a forward tilt position, or fixed to the tilt controlhousing 3 in some manner. Preferably, the back 5 is first secured to thetilt control housing 3 and the seat 4 is then fixed to the back 5. Thetilt lock device 28 performs the first function, and the seat lockdevice 105 performs the second function.

[0069] In operation, the back support member 6 is first fixed to thetilt control housing 3 using the tilt lock device. The actuator deviceis then employed to release the lock bar 47, thereby permitting the seat4 to tilt upwardly into a forward tilt position where it is locked inposition by the seat lock device 105. Therefore, the tilt lock device 28and the seat lock device 105 must be employed in a specific order. Usinga single handle ensures that this sequence is performed in the correctorder. For example, an outward pull of the handle 43 will first engagethe tilt lock device 28 as previously described. As shown in FIGS. 2 and16, an end of the seat lock cable 63 extends past the bracket 153 whilethe tilt lock cable 42 is attached to the bracket 153. Therefore, anoutward pull on the handle 43 pulls the tilt lock cable 42 but does notpull the seat lock cable 63. A further extension of the handle 43,however, pulls the tilt lock cable 42 until the bracket 153 engages theend of the seat lock cable 63, thereby causing the actuator device torelease the seat 4 and permitting it to rotate into a forward tiltposition. When the seat 4 is positioned in the forward tilt position,the handle 43 is released and the lock bar 47 is biased into the firstslot 54 by the springs 57, thus securing the seat 4 to the supportmember 6.

[0070] In an exemplary embodiment, shown in FIGS. 11 and 12, the seat 4includes a shell 64, a seat bracket 69, and a seat adjustment device 73.The seat bracket 69 has four elongated openings 71 and a plurality ofteeth 70. The shell 64 has four mounting pads 113 and a mounting hole115 positioned in each pad 113. The shell 64 is slidably mounted to theseat bracket 69 by installing four fasteners 72 in the elongatedopenings 71 as shown in FIG. 14. The fasteners 72 engage the shell atthe mounting holes 115. Each fastener includes a cap 82 and a shaft 83.The fasteners secure the shell 64 to the seat bracket 69 whilesimultaneously permitting the shell to translate forwardly andrearwardly with respect to the seat bracket 69. During translation, theshaft 83 of the fastener slides in the elongated opening 71 while thecap 82 secures the shell 64 to the seat bracket 69.

[0071] The seat adjustment device includes a lever 74 and a spring 76.The lever 74 slidably engages a housing portion 66 of the shell 64,which includes two straps 121 and an outer shell 125. The spring 76 isdisposed in the housing 66 and operably engages a bearing member 141extending upwardly from the lever 74. The spring 76 also operablyengages the housing 66, as shown in FIGS. 12 and 13. In an exemplaryembodiment, shown in FIGS. 12 and 13, the spring is a compression springbiasing an end portion 143 of the lever 74 against the teeth 70. It isunderstood that other embodiments could use a tension spring. To actuatethe seat adjustment device, the user pulls a handle 145, that extendsoutwardly from the lever 74, away from the teeth 70, thereby disengagingthe end portion 143 of the lever 74. The user then translates the shell64 in a forward or rearward direction until the desired seat depthposition is obtained. The lever 74 is then released. When released, thespring 76 biases the end portion 143 of the lever 74 against the teeth70 and into an engaged position, thereby preventing the shell 64 frombeing translated in a forward or rearward direction.

[0072] Although the present invention has been described with referenceto preferred embodiments, those skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. As such, it is intended that the foregoingdetailed description be regarded as illustrative rather than limitingand that it is the appended claims, including all equivalents thereof,which are intended to define the scope of the invention.

We claim:
 1. A chair adapted to move between an upright position and areclined position, comprising: a base including a tilt control housingmounted thereon; a seat pivotally attached to the tilt control housingabout a first horizontal axis so as to allow the seat to be rotatedthrough a first angle as the chair moves between the upright positionand the reclined position; a back pivotally attached to the tilt controlhousing about a second horizontal axis positioned rearwardly of saidfirst horizontal axis so as to allow the back to be rotated through asecond angle as the chair moves between the upright position and thereclined position, said back having a forwardly extending supportmember; a torsion spring having a forwardly extending leg and arearwardly extending leg, said forwardly extending leg mounted to saidtilt control housing; a first slide member disposed on one of the seatand the support member, said slide member adapted to slidably engage theother of said seat and said support member; a second slide memberdisposed on one of the support member and the rearwardly extending legof the torsion spring, said second slide member adapted to slidablyengage the other of said support member and rearwardly extending leg ofthe torsion spring; a tilt limiter device adapted to limit upwardtilting of the back; whereby a rotation of the seat through the firstangle as the chair moves between the upright position and the reclinedposition causes the back to rotate through a second angle, and whereinthe second angle is larger than the first angle.
 2. The chair of claim 1wherein said tilt limiter device comprises a stop member disposed on thesupport member and a catch member disposed on the tilt control housing,said stop member adapted to releasably engage said catch member to limitupward tilting.
 3. The chair of claim 1 wherein said torsion spring hasa horizontal axis spaced apart from the second horizontal axis.
 4. Thechair of claim 1 wherein the first slide member is fixedly mounted to anunderside of the seat for slidable engagement with the support member,and the second slide member is fixedly mounted to an underside of thesupport member for slidable engagement with the rearwardly extending legof the torsion spring.
 5. The chair of claim 1 wherein the first slidemember is fixedly mounted to an underside of the seat for slidableengagement with the support member, and the second slide member isdisposed on the rearwardly extending leg of the torsion spring forslidable engagement with the underside of the support member.
 6. Thechair of claim 1 wherein the first slide member is fixedly mounted to atop surface of the support member for slidable engagement with theunderside of the seat, and the second slide member is disposed on therearwardly extending leg of the torsion spring for slidable engagementwith the underside of the support member.
 7. The chair of claim 1wherein the first slide member is fixedly mounted to a top surface ofthe support member for slidable engagement with the underside of theseat, and the second slide member is fixedly mounted to an underside ofthe support member for slidable engagement with the rearwardly extendingleg of the torsion spring.
 8. The chair of claim 4 wherein the torsionspring comprises a pair of forwardly extending arms adjustably mountedto a forward portion of the tilt control housing, and a pair ofrearwardly extending arms having end portions coupled together by ablock member.
 9. The chair of claim 8 wherein the second slide memberand the block member are configured as complementary wedge-shapedmembers.
 10. The chair of claim 9 wherein the first and second slidemembers are acetal and the block member is nylon.
 11. The chair of claim1 further comprising a coupling block mounted to the seat and adapted toslidably engage the support member, whereby the seat and the supportmember are maintained in a proximate relationship as the chair movesbetween the upright position and the reclined position.
 12. The chair ofclaim 1 further comprising a tilt lock device adapted to releasably lockthe back to the tilt control housing in a plurality of positions. 13.The chair of claim 12 wherein said tilt lock device comprises a lockmember depending downwardly from the support member; a guide membermounted to said tilt control housing, said guide member having a guidehole; and a lock pin slidably received in said guide hole; said lockmember having a plurality of openings adapted to receive said lock pin,said lock pin selectively engaging said lock member at one of saidopenings.
 14. The chair of claim 13 wherein said plurality comprises anupper slot, wherein said support member and said back are maintained ina reclined position when said lock pin engages said lock member at saidupper slot.
 15. The chair of claim 13 wherein said tilt lock devicefurther comprises a handle, an actuator spring, a cable connecting thehandle and the actuator spring, an end bracket connecting said actuatorspring and said lock pin, a disengagement spring, and a lock washer, andwherein said guide member also has a cavity, said cavity communicatingwith said guide hole such that a portion of said lock pin is positionedin said cavity, said disengagement spring disposed on said lock pinwithin said cavity, and wherein said lock washer is disposed on saidlock pin, said lock washer capturing said disengagement spring disposedon said lock pin between said lock washer and a surface defining thecavity.
 16. The chair of claim 1 wherein the seat is adapted to tiltforwardly into a forward position such that the first slide memberdisengages the support member.
 17. The chair of claim 16 furthercomprising a seat lock device adapted to secure the seat to the supportmember in a forward tilt position.
 18. The chair of claim 16 furthercomprising a stop device adapted to operably engage the seat and thetilt control housing to hold the seat in a forward tilt position. 19.The chair of claim 18 wherein the stop device comprises a tilt lockdevice adapted to secure the support member to the tilt control housingin a locked position, and a seat lock device adapted to secure the seatto the support member in a forward tilt position.
 20. The chair of claim19 further comprising a front torsion spring having a first leg biasedagainst a forward portion of the seat and a second leg mounted to thetilt control housing.
 21. The chair of claim 20 wherein said seat lockdevice further comprises a tilt bracket extending downwardly from theseat, and a lock bar, said tilt bracket having a first slot, a secondslot and a channel in communication with said slots, and wherein saidsupport member has a support slot substantially aligned with one of thefirst slot, the second slot and the channel as the seat rotates aboutsaid first horizontal axis of rotation, wherein said lock bar engagessaid support member at said support slot, and wherein said lock barengages said tilt bracket at one of said first slot or said second slot.22. The chair of claim 21 wherein said lock bar engages said tiltbracket at said first slot, whereby the seat is locked in a forward tiltposition.
 23. The chair of claim 21 wherein said lock bar engages saidtilt bracket at said second slot, whereby the seat and the supportbracket are maintained in a proximate relationship as the chair movesbetween the upright position and the reclined position.
 24. The chair ofclaim 21 further comprising a spring connecting the lock bar and aforward edge of the support member, said spring biasing the lock barinto one of the first slot and the second slot, and an actuator devicemounted to the support member, said actuator device adapted to retractthe lock bar from one of the first slot and the second slot into thechannel.
 25. The chair of claim 24 wherein said actuator devicecomprises a slide bracket slidably mounted to said support member andconnected to said lock bar, a lever arm rotatably mounted to saidsupport member, a handle, and a cable connecting the handle and a firstend of the lever arm, said lever arm having a second end connected tothe slide bracket, whereby an outward pull on the handle causes thecable to rotate the lever arm, which causes the third slide member tomove rearwardly, which causes the lock bar to be retracted from one ofthe first slot and the second slot into the channel.
 28. The chair ofclaim 17 wherein said seat lock device further comprises a tilt bracketextending downwardly from the seat, and a lock bar, said tilt brackethaving a first slot, a second slot and a channel in communication withsaid slots, and wherein said support member has a support slotsubstantially aligned with one of the first slot, the second slot andthe channel as the seat rotates about said first horizontal axis ofrotation, wherein said lock bar engages said support member at saidsupport slot, and wherein said lock bar engages said tilt bracket at oneof said first slot or said second slot.
 29. A chair adapted to movebetween a forward position, an upright position and a reclined position,comprising: a base including a tilt control housing mounted thereon; aseat pivotally attached to the tilt control housing about a firsthorizontal axis so as to allow the seat to be rotated through a firstangle as the chair moves between the upright position and the reclinedposition; a back pivotally attached to the tilt control housing about asecond horizontal axis positioned rearwardly of said first horizontalaxis so as to allow the back to be rotated through a second angle as thechair moves between the upright position and the reclined position, saidback having a forwardly extending support member; a torsion springhaving a forwardly extending leg and a rearwardly extending leg, saidforwardly extending leg mounted to said tilt control housing; a firstslide member disposed on one of the seat and the support member, saidslide member adapted to slidably engage the other of said seat and saidsupport member; a second slide member disposed on one of the supportmember and the rearwardly extending leg of the torsion spring, saidsecond slide member adapted to slidably engage the other of said supportmember and rearwardly extending leg of the torsion spring; a tiltlimiter device adapted to limit upward tilting of the back; wherein saidseat is adapted to tilt forwardly through a third angle into saidforward position such that the first slide member disengages one of thesupport member and seat; and whereby a rotation of the seat through thefirst angle as the chair moves between the upright position and thereclined position causes the back to rotate through a second angle, andwherein the second angle is larger than the first angle and whereby arotation of the seat through the third angle as the seat moves betweenthe upright position and the forward position does not cause the back torotate through any angle.
 30. The chair of claim 29 further comprising ablock member coupling end portions of the rearwardly extending legs ofthe torsion spring, and wherein the first slide member is fixedlymounted to an underside of the seat for slidable engagement with thesupport member, and wherein the second slide member is fixedly mountedto an underside of the support member for slidable engagement with theblock member, and wherein the second slide member and the block memberare configured as complementary wedge-shaped members.
 31. The chair ofclaim 29 further comprising a tilt lock device adapted to releasablylock the support member to the tilt control housing in a plurality ofpositions.
 32. The chair of claim 31 wherein said tilt lock devicecomprises a lock member depending downwardly from the support member, aguide member mounted to said tilt control housing, said guide memberhaving a guide hole, and a lock pin slidably received in said guidehole, said lock member having a plurality of openings adapted to receivesaid lock pin, said lock pin selectively engaging said lock member atone of said openings.
 33. The chair of claim 29 further comprising astop device adapted to operably engage the seat and the tilt controlhousing to hold the seat in a forward tilt position.
 34. The chair ofclaim 33 wherein the stop device comprises a tilt lock device adapted tosecure the support member to the tilt control housing in a lockedposition, and a seat lock device adapted to secure the seat to thesupport member in a forward tilt position.
 35. The chair of claim 34further comprising an front torsion spring having a first leg biasedagainst a forward portion of the seat and a second leg mounted to thetilt control housing.
 36. The chair of claim 35 wherein said seat lockdevice comprises a tilt bracket extending downwardly from the seat and alock bar, said tilt bracket having a first slot, a second slot and achannel in communication with said slots, and wherein said supportmember has a support slot substantially aligned with one of the firstslot, the second slot and the channel as the seat rotates about saidfirst horizontal axis of rotation, wherein said lock bar engages saidsupport member at said support slot, and wherein said lock bar engagessaid tilt bracket at one of said first slot or said second slot.
 37. Thechair of claim 36 wherein said lock bar engages said tilt bracket atsaid first slot, whereby the seat is locked in a forward tilt position.38. A chair adapted to be locked in a plurality of positions, includingan upright position and a reclined position, comprising: a baseincluding a tilt control housing mounted thereon; a seat pivotallyattached to the tilt control housing about a first horizontal axis so asto allow the seat to be rotated through a first angle as the chair movesbetween the upright position and the reclined position; a backcomprising a support member pivotally attached to the tilt controlhousing about a second horizontal axis positioned rearwardly of saidfirst horizontal axis so as to allow the back to be rotated through asecond angle as the chair moves between the upright position and thereclined position, said support member slidably engaging said seat; atorsion spring having a forwardly extending leg and a rearwardlyextending leg, said forwardly extending leg mounted to said tilt controlhousing, said rearwardly extending leg slidably engaging said supportmember; a tilt limiter device adapted to limit upward tilting of theback; and a tilt lock device comprising a lock member dependingdownwardly from the support member, a guide member mounted to said tiltcontrol housing, said guide member having a guide hole, and a lock pinslidably received in said guide hole, said lock member having aplurality of openings adapted to receive said lock pin, said lock pinselectively engaging said lock member at one of said openings.
 39. Achair adapted to move between an upright position and a reclinedposition, comprising: a base including a tilt control housing mountedthereon; a seat pivotally attached to the tilt control housing about afirst horizontal axis so as to allow the seat to be rotated through afirst angle as the chair moves between the upright position and thereclined position; a back pivotally attached to the tilt control housingabout a second horizontal axis positioned rearwardly of said firsthorizontal axis so as to allow the back to be rotated through a secondangle as the chair moves between the upright position and the reclinedposition, said back having a forwardly extending support member; atorsion spring having a horizontal axis spaced apart from the secondhorizontal axis of rotation, said spring having a forwardly extendingleg and a rearwardly extending leg, said forwardly extending leg mountedto said tilt control housing; a first slide member disposed on one ofthe seat and the support member, said slide member adapted to slidablyengage the other of said seat and said support member; a second slidemember disposed on one of the support member and the rearwardlyextending leg of the torsion spring, said second slide member adapted toslidably engage the other of said support member and rearwardlyextending leg of the torsion spring; and a tilt limiter device adaptedto limit upward tilting of the back; whereby a rotation of the seatthrough the first angle as the chair moves between the upright positionand the reclined position causes the back to rotate through a secondangle, and wherein the second angle is larger than the first angle. 40.The chair of claim 39 further comprising a tilt lock device adapted toreleasably lock the back to the tilt control housing in a plurality ofpositions.
 41. The chair of claim 39 wherein the seat is adapted to tiltupwardly such that the first slide member disengages the support member.42. The chair of claim 41 further comprising a seat lock device adaptedto secure the seat to the support member in a forward tilt position. 43.The chair of claim 41 wherein the stop device comprises a tilt lockdevice adapted to secure the support member to the tilt control housingin a locked position, and a seat lock device adapted to secure the seatto the support member in a forward tilt position.
 44. The chair of claim1 wherein said seat further comprises: a shell having a housing; a seatbracket having an adjustment slot and a plurality of teeth; a fastenerslidably mounting said shell to said seat bracket, said fastenerengaging said seat bracket at said adjustment slot; a spring disposed inthe housing; a lever disposed in the housing, said lever adapted toengage said teeth of said seat bracket, said lever adapted to operablyengage said spring, said lever biased against said teeth by said spring.45. A chair comprising: a base; a seat comprising a shell and a seatbracket, said shell having a housing, said seat bracket having anadjustment slot and a plurality of teeth, said seat bracket attached tosaid base; a fastener slidably mounting said shell to said seat bracket,said fastener engaging said seat at said adjustment slot; a springdisposed in said housing; a lever adapted to engage said teeth of saidseat bracket, said lever disposed in said housing, said lever adapted tooperably engage said spring, said lever biased against said teeth bysaid spring.